Moving the radiator to the other side of the support may require you to remove the diagonal cross members and the top part of the radiator.

Fixing the mount bracket might be easier. If the shop has already done it once but it wasn't enough, it should be easy for them to move them again.

Another possibility might be to shorten your already short waterpump. Using a press you could move the bolt surface on the pump closer to the block by 1/2 an inch. Then all you'd need is a different pulley to line up the belts.

'51 Chevy 1/2 ton w/'62 261, HEI, offy, fentons, dual carter/webbers, t-5 & 12 bolt posi